Which of the Following Is an Example of Track-Two Diplomacy

Which of the following is an example of track-two diplomacy?

A) the United States simultaneously negotiating with a foreign government and that state's domestic interest groups
B) a Norwegian sociologist's efforts to reconcile relations between Israel and the Palestine Liberation Organization
C) U.S. President Woodrow Wilson's Fourteen Points and the Treaty of Versailles
D) the United States threatening Iran with sanctions and invasion
E) Soviet and Americans leaders meeting at a summit